1. Field of the Invention
The present invention relates to an inkjet recording head that can be packaged at high density and an inkjet recording apparatus using the inkjet recording head.
2. Background Art
Along with the spread of personal computers and the development of graphic processing programs, there is a demand for outputting not only the characters but also the hard copy with high quality of image. Also, there is a great demand for on-demand printing in the placard or large poster printing field, whereby the on-demand inkjet recording apparatus has been broadly used.
A printing head for use in the on-demand inkjet recording apparatus is largely classified into three kinds of structures. A first structure is a so-called thermal inkjet printing head in which a heater for vaporizing the ink instantaneously is provided at the top end of nozzle to produce flying ink droplets owing to an expansion pressure at the time of vaporization.
A second structure involves using a shear mode deformation of piezoelectric element in which a piezoelectric element is provided in a container forming an ink reservoir to produce flying ink droplets owing to a pressure caused when the piezoelectric element is deformed upon an applied signal.
A third structure involves using an electrostatic adsorption, instead of a piezoelectric vibrator, in which a piezoelectric element is disposed opposed to a pressure generating chamber making an ink reservoir to produce flying ink droplets owing to a dynamic pressure caused in the pressure generating chamber by expansion and contraction of the piezoelectric element.
In JP-A-6-8422, one example of the on-demand inkjet recording head of the third type was disclosed. This third structure involves flying ink droplets by using a deformation of piezoelectric element in which piezoelectric elements are packaged opposed to an ink chamber composed of a plurality of chamber plates laminated, a chamber plate having a plurality of nozzle openings arranged in a row. In the case of this recording head, there is a problem that if the nozzle packaging density, or a so-called nozzle-to-nozzle pitch interval, is decreased, the pitch of the ink chamber or the piezoelectric element is naturally smaller.
To solve this problem, JP-A-2000-289233 has proposed a method in which a plurality of rows of nozzles are arranged within one head, and the nozzle positions in each row are shifted, thereby increasing the printing density in which data is printable per one scan.
However, with this method, since a plurality of rows of nozzles are formed in one plate, the piezoelectric vibrators must be packaged opposed to each row of nozzles.
As another conventional example with the increased packaging density of nozzles, a structure as shown in FIG. 12 is well known. This recording head comprises a nozzle plate 11 having a plurality of nozzle openings 16, and a chamber plate 12 with the pressure generating chambers 18 arranged in alternately staggered form, corresponding to the plurality of nozzle openings 16 arranged on the nozzle plate 11, in which the piezoelectric elements 23 divided like a comb are securely disposed opposed to the pressure generating chambers 18 sealed with a diaphragm 13.
In this constitution, since the pressure generating chambers 18 are disposed in staggered form, the corresponding piezoelectric elements 23 are also disposed in staggered form. That is, since two groups of piezoelectric elements must be precisely inserted and secured at very proximate positions, there is a problem that the operability of assembling is bad.
In packaging the nozzles of the inkjet recording head at high density to increase the number of nozzles, it is necessary to enhance the workability and the operability of assembling. If the number of parts or aligning positions is increased, the precision is lowered, making it difficult to fabricate the high quality inkjet recording head stably.
The structure in which a plurality of row of nozzles are arranged on one plate to attain a higher packaging density has a problem that a group of vibrators are required for each row of nozzles, and there are a number of aligning positions, resulting in the bad workability and the higher cost. Also, since the printing occurs only in the direction along which the plurality of rows of nozzles are arranged, the line recording apparatus of head fixed type has only a packaging structure in which the heads are arranged in staggered form. Also, it is difficult to avoid a problem that the area of head portion is so large that a head preservation portion or the entire apparatus is increased in size.
The conventional example as shown in FIG. 12 has a problem that the workability is bad, because it is required to shift and fix two groups of piezoelectric elements in a very narrow area at high precision.